Cement mortar and resin mortar are known as mortar compositions used for applications such as joint materials and finish materials for concrete surfaces. A cement mortar is a mixture obtained by adding an aggregate and water to cement, such as portland cement or blended cement, and mixing the same and is used mainly in spraying the surface of a slope of cut or fill, or as a concrete adjusting material. Of such cement mortar, commonly used types are 1:2 mortar whose cement to aggregate ratio is 1 to 2, and 1:3 mortar whose cement to aggregate ratio is 1 to 3.
On the other hand, resin mortar is a mixture obtained by mixing resin (organic adhesive), such as styrene-butadiene rubber latex (SBR), ethylene-vinyl acetate (EVA) or polyacrylic ester (PAB) emulsion, into the above described cement mortar. As a result of mixing resin into the cement mortar, the resin mortar has improved properties in bonding strength, flexural strength and resistance to acids. Therefore, it is suitably used in sealing decoration materials or repairing floor, wall and the like.
However, a bonding strength of a cement mortar is generally as low as 0.3 N/mm2 to 0.5 N/mm2. The strength is far lower than the value 2.0 N/mm2, which is considered to be preferable from the viewpoint of seismic safety, and does not even reach the value 1.2 N/mm2, which is considered as a measure of daily safety. Moreover, it is susceptible to expansion/contraction because of its high water absorption properties, and repeated expansion/contraction results in its deterioration, causing peeling or cracking.
On the other hand, bonding strength is increased with regards to resin mortar as a result of mixing resin to cement mortar. However, since the properties of a resin itself remains, deterioration due to the environmental factors, such as ultraviolet rays and rainwater, is significant. Accordingly, if a larger amount of resin is used for resin mortar to obtain satisfactory bonding strength, the resin mortar deteriorates more significantly due to the environmental factors, resulting in poor durability, and cannot be used for practical applications. Moreover, since resin itself is combustible, resin mortar is not suitable to be used in places where it may cause a fire. In addition, it raises many problems, such as causing rashes when the resin attaches to a person's skin, and environmental pollution due to the volatilization of organic solvent.
As recent prior arts, Japanese Patent Laid-Open No. 11-092205 discloses a mortar composition combining high compressive strength and low static modulus of elasticity, and Japanese Patent Laid-Open No. 2000-072518 discloses spraying cement having high flowing properties.
However, the present condition is that no invention has been made yet which relates to a mortar composition meeting all the requirements of high bonding strength, high compressive strength, high strain level and high flexural strength, and capable of being provided at low cost.
This invention has been made in light of the above described problems, and accordingly, an object of this invention is to provide a mortar composition having sufficiently high bonding strength to fulfill the standard of seismic safety, and also having high strain level.
Another object of this invention is to provide a mortar composition having high compressive strength, high flexural strength and high follower properties, and in addition, not being susceptible to cracks.
Another object of this invention is to provide a mortar composition not susceptible to expansion/contraction, and has limited changes with time (deterioration due to elapsing time).
Still another object of this invention is to provide a mortar composition considering the safety of operation by using no organic adhesives, and the use of other organic materials and volatile solvents is avoided as much as possible.
Another object of this invention is to provide a mortar composition which allows low material costs and high workability.
The other objects, features and advantages of the invention will be better understood by those skilled in the art from the following description.